A new study of chitin synthetase 3 from yeast has led to the conclusion that under certain conditions this enzyme, like chitin synthetases 1 and 2, behaves as a zymogen. Of the three genes necessary for chitin synthetase 3, only CAL1/CSD2 and CAL3 are required for the zymogenic activity, whereas the product of CAL2 appears to act as an activator. A method for the simultaneous determination of the three yeast synthetases in a mixture has been developed. The GTPase activity of a GTP-binding protein that regulates beta(1- >3)glucan synthetase has been found to be modulated by an apparent GTPase activating protein (GAP) that may link cell wall synthesis with cell cycle controls. Identification of the linkage between chitin and beta(1->3)glucan in the yeast cell wall has been completed.